Method and apparatus for heating formed products



METHOD AND APPARATUS FOR HEATING FORMED PRODUCTS- A. M. COOK Dec. 10, 1968 Filed Dec.

2 Sheets-Sheet l Fzghl A. M. COOK Dec. 10,v 196s METHOD AND APPARATUS FOR HEATING FORMED PRODUCTS 2 Sheets-Sheet 2 Filed Dec.

INVE T R AEA/OLD AH? BLOWER United States Patent O' 3,415,505 METHOD AND APPARATUS FOR HEATING FORMED PRODUCTS Arnold M. Cook, Holden, Mass., assignor to Norton Company, Worcester, Mass., a corporation of Massachusetts Filed Dec. 29, 1966, Ser. No. 605,908 Claims. (Cl. 263-36) ABSTRACT OF THE DISCLOSURE This invention relates generally to an improved method for firing, sintering or otherwise heat treating a wide variety of products such as grinding wheels, dinnerware, ceramic tile and the like earthenware, and refractory products and apparatus for carrying out the method. The invention is particularly concerned with the method of heat treating formed products by establishing two bodies of hot gas rotating in opposite directions in rolling contact with each other about parallel vertical axes, and an apparatus for carrying out the method comprising a continuous vertical gas red kiln having two intersecting e1- liptical heating chambers in communication with each other along their adjacent sides.

Background of the invention In the continuous kilns of the prior art, the products being heated are supported on kiln cars, other refractory supports or kiln cars in combination with refractory supports, and are usually moved horizontally through controlled temperature zones. It is diicult to achieve uniformity of temperature from side to side and top to bottom in a load of supported products passing through horizontal kilns such as tunnel type kilns. The flow of gases around the products is usually at a low velocity with a resulting uneven heating and low rate of heat transfer. Because of the problems inherent in the operation of tunnel kilns and in order to reduce the temperature gradient within, the kilns are usually made relatively long. This construction is costly, requires long cycles, has high heat losses, presents diticult temperature control problems and requires large areas of floor space.

Since the difficulties of the prior art kilns are due primarily to the fact that the direction of the gravitational field is transverse to the direction of movement of the formed articles, and since the direction of the gravitational teld cannot be changed, the only remaining possibility is to change the direction of movement of the formed products by moving them vertically instead of horizontally during their heat treatment. Since the gravitational eld will then be along the length of the kiln instead of in the transverse' direction, the ow paths of the hot gases will then also be completely different and can be made to follow uniform helical paths longitudinally along opposite sides of the kiln and in rolling contact along the central axis of the kiln. The high degree of symmetry of the ow pattern thus obtained is diticult if not impossible to obtain in a horizontal kiln where the gravitational field is transverse to the axis of the kiln.

Vertical kilns are also known and such kilns are disclosed in U.S. Patents Nos. 66,464; 317,351; 826,831; 1,939,054 and 3,091,833, the disclosures of which are incorporated herein. None of the prior art patents related to vertical kilns disclose the concept of heat treating the products with two bodies of hot gas rotating in opposite directions in rolling contact with each other about parallel vertical axes nor are vertical kilns for carrying out the method disclosed.

3,415,505 Patented Dec. 10, 1968 rice Description of the invention It is therefore an object of the present invention to reduce the time required to fire, sinter or treat formed products in a kiln by providing a method and apparatus for directing the flow of the heating gases at relatively high velocities and turbulence to increase the eiciency and rate of heat transfer.

Another object of the invention is to provide for a gradual increase and decrease in the temperature of the product with a minimum temperature gradient within the product.

A further object of the invention is to provide an improved vertical kiln having maximum flexibility for controlling the heating of a wide selection of formed products.

Still a further object of the invention is to provide for the controlled flow of air and gases giving optimum utilization of heat and improved thermal eiiiciency.

It is a further object of the invention to provide a kiln having optimum utilization of heat with a minimum heat loss and a minimum requirement for floor space.

Further objects and the broad concept of the invention will become obvious from a consideration of the specication, claims and the accompanying drawings wherein:

FIGURE 1 is a vertical section through the kiln with the product supports in position therein;`

FIGURE 2 is a plan view of the kiln with portions of the associated conveyors and with the top surface plate cut away to show the configuration of the central passageway.

FIGURE 3 is a horizontal cross section through the kiln with parts left out to more clearly show the configuration of the interior passageway and of the openings in both the top and bottom end covers of the kiln; and

FIGURE 4 is a perspective view of the main central element of the kiln showing the opposed elliptical passageways extending therethrough.

With particular reference to FIGURE l, the kiln proper is shown comprising a vertical cylindrical structure 1 supported on legs 2 and provided with an open central passageway 3 that is enlarged at opposite sides throughout the entire interior length of the kiln between the top and l'bottom plates wherein the passageway conforms to but slightly larger than the shape of' the batts passing therethrough. These enlarged spaces 4 and 5 are elliptical in cross section with their major axes parallel to each other and with the contiguous portions of the elliptical areas overlapping each other. Air admission conduits 6 open tangentially into the elliptical areas at the top of the kiln and in opposite directions at the two sides so that the two rotating bodies of air in the two elliptical spaces will be in rolling contact with each other. At the lower end of the kiln there are two similarly positioned conduits 7 connected to an exhaust fan for removing the hot gases containing the products of combustion of the hydrocarbon fuel such as natural gas introduced by nozzles 8 at or near the middle of the kiln and in the same tangential direction as the air from above which has become heated by the loaded supports having hot articles thereon.

A hydraulic jack 9 is provided beneath the column of supports or batts 10 on which the grinding Wheels or other formed products 11 to be heat treated are carried. Whenever .another `support or batt is to be added to the column, the additional support is first placed on the jack and the latter is then expanded to support the load with the additional support in contact lwith the support above the level of the stack-supporting dogs 12 which are then actuated in Aany suitable m'anner as by cylinders 13 to rst move radially outwardly to allow further upward movement of the jack and support thereon and then inwardly into stack-supporting position before retraction of the jack 9.

At the upper end of the kiln, the supports or batts previously added to the bottom of the stack and which have passed through the heat treatment and cooling process are supported by a plurality of pivotable dogs 14 actuated by any suitable means `such as a solenoid, motor, or hydraulic cylinder 14 in the proper loading and unloading sequence. These batts are then taken olf from the top of the stack by pick-off dogs 14 carried by a radial .arm 15 capable of being raised and lowered by mechanism 16 of any suitable kind, preferably a cable hoist actuated by a motorized Winch 17. The radial arm is slidable up or down a splined shaft 18 which can be slowly rotated in one direction or the other by a motorized reduction gearing 19 or any other suitable means such as a rotary hydraulic motor. Convey-ors 20 and 21 are provided for movin-g the supports or batts twith the formed products thereon to and from the kiln respectively.

As shown in FIGURE 2, each of the batts 10 carries three equally spaced peripheral spacing blocks Z2 for carrying the batts above it with sufficient distance between the products on each batt and the bottom of the batt immediately above it to permit free horizontal circulation of air or gas in the elliptical spaces and across the two halves of each loaded batt.

Preferably the bottom entrance and the top exit portions of the kiln each have an end plate having an opening of slightly larger configuration than that of the aligned batts 10 to prevent excessive leakage of gases therethrough.

In a method of using the embodiment of the invention shown in the figures, a support 10 comprising an aluminum oxide or silicon carbide refractory batt and having an unred grinding wheel 11 supported thereby is placed on loading conveyor 20. Support blocks 22, which may vary in shape and thickness, are located at the corners of the batt to provide stability, spacing and circulation between successive batts. The loaded batt is rolled from the conveyor into position over the head of hydraulic jack 9 and the fjack is actuated. The support blocks 22 of this batt contact the bottom of the batt of the sack of batts supported by support dogs 12 and then the newly fed in support blocks 22 and grinding wheel 11 .and the stack are lifted by the upward stroke of the piston. The support dogs 12 `are removed to permit the successive batts to be moved into the bottom of chamber 3 as the stack is lifted, and `dogs 12 are then repositioned to hold the stack in a stationary position during the downward return stroke of the ypiston of the jack.

Air is introduced through conduit 6 by means of `a blower at the top of the kiln. Hydrocarbon gas, such *as natural gas, is introduced through conduit 8 approximately at the center of the vertical height of the kiln and in a direction to continue the circulating motion of the gases. Combustion takes place .as the natural gas combines with the preheated air and a hot zone or zone of highest temperature is defined in the kiln. The exhaust gases are Withdrawn through conduits 7 at the bottom of the kiln by .means of an exhaust fan in a direction continuing the circulating motion started at the top of the kiln. As the air introduced at the top of the kiln is carried downward in two spiral paths to the hot zone, it is heated by contact with the grinding wheels and supports. As the air is heated the grinding wheels and supports are cooled. From the hot zone downward a counter current heating process takes place between the products of combustion and the grinding wheels and supports.

As a result of the stack having been raised the height of one batt by insertion of a green wheel at the bottom of chamber 3 by the action of the jacks, a treated or fired grinding Wheel and its batt are lifted above the top of the kiln to be available for removal from the kiln. The

uppermost batt is then engaged by pick-olf dogs 14 and radial arm 15 is then rotated into position over unloading conveyor 21. The radial arm is loxwered by mechanism 16 and the red grinding wheel and batts are positioned on the unloading conveyor `whereupon the cylinder 14 is actuated to swing the dogs 14 out of engagement with the batt so the pick-up means can be returned to the top of the kiln.

Because of the counter current heating process and the improved heat transfer resulting from the velocity of the gases, new .and unexpected results are inherent in the operation of the kiln the most important of which resides in the very high thermal efliciency attained. The preheating of the air prior to combustion is one important feature found in the concept of the invention here shown and adds materially to the improved eiciency and rapid production of high temperatures within chamber 3. Because of high heat transfer rates, low temperature gradients exist Within the product and a relatively short kiln and stack height may be used resulting in shortened cycle times.

In a typical example of tiring grinding wheels 14" in diameter by 1 thick composed of 46 grit aluminum oxide abrasives and a clay bond pressed to 5000 pounds per square inch, the green Wheels are placed on their respective batts and lifted into the kiln. The kiln chamber is about six feet high ,and when filled contains approximately 30 wheels and batts. The green wheels are inserted at the bottom and tired wheels are removed at the top at a rate of one per minute, resulting in a total cycle time of about 30 minutes per wheel. The highest temperature (2400 F.) is reached in the middle of the vertical height Eand it takes about l5 minutes to heat each wheel from room temperature to 2400 F.

Atmospheric air is fed into two tangential entrance ducts at the top of the kiln chamber by means of a fan at a rate of about 300 cu. ft. per minute and at a velocity of 3000 feet per minute. The cyclonic spiraling paths of air pass through the space between the wheel and batt at a velocity of about 1200 ft. per minute at the top of the kiln and gradually increases in velocity as it is heated by the Ware and expands, so that it reaches about 6000-7000 ft. per minute at the center of the kiln where it combines with natural gas for combusion.

Gas is fed into the center of the kiln through two nozzles about g" diameter at a rate of about one cubic vfoot per minute and a velocity of 3000 ft. per minute. The nozzles are directed into the chamber tangentially and in the same direction as the air flow to continue the spiraling action. Combustion takes place in the annular space between the wall and stack of wheels as the -g-as combines with the heated air.

The products of combustion and heated air continue to spiral downwardly from the 2400" F. hot zone to the two tangential exit ducts at the bottom of the kiln, transferring the heat to the wheels and batts in their path. The exit ducts are connected to an exhaust fan and are arranged tangentially to assist in maintainin-g the cyclonic action. The air and products of combustion are exhausted at a velocity of about 3000 ft. per minute and at a temperature of about 200 F.

By this action the wheels lare heated at an average rate of F. per minute from room temperature to 2400 F. in 15 minutes and cooled at about the same rate from 2400 F. to about 200 F. in 15 minutes.

The method and apparatus of the present invention provide simplicity of operation and construction, low initial cost and low operating and maintenance cost. The floor space occupied by the kiln is only a fraction of the space occupied by conventional tunnel kilns of equal capacity. The speedy tiring cycle and vertical kiln arrangement herein described, may be easily integrated with preceding or subsequent wheel manufacturing operations. It is to be noted that the rapid tiring cycle reduces the total number of supports or batts required `for production of a given number of wheels in a given time period as compared with the number required for the operation of a conventional tunnel kiln.

It will be understood that this invention is susceptible to modication in order to adapt it to diEerent usages and conditions and, accordingly, it is suggested that many of such modifications may fall `within the scope of the following claims.

I claim:

1. The method of heat treating formed products in a kiln comprising:

(a) establishing two elliptical tbodies of hot gas rO- tating in opposite directions in rolling contact with each other about parallel axes;

(b) flowing said two bodies along helical paths around said axes; and

(c) simultaneously moving the formed products between said axes in the region of rolling gaseous contact.

2. The method of claim 1 wherein said bodies rotate about vertical axes, and said products move between said axes.

3. The method of claim 2 wherein the bodies move downwardly in a helical path around said vertical axes, and said products move upwardly between said axes.

4. An apparat-us for heat treating formed products comprising:

(a) two intersecting substantially elongated Vgenerally parallel heating chambers in communication with each other along their adjacent sides;

(b) means for introducing an oxygen-containing gas into each chamber to rotate tangentially in opposite directions, at one end of the kiln, so that the gas in one chamber rotates clockwise while the gas in the other chamber rotates counterclockwise;

(c) means `tor injecting a combustible fluid tangentiaL ly into said chambers;

(d) means Ifor removing gaseous products of combustion tangentially from each of said chambers at CFI the end opposite to the in-feed end of the respective chambers; and

(e) means for moving a series of batts holding formed product to be fired, the batts being moved in spaced relation to one another between said chambers.

5. The apparatus of claim 4 where in said chambers are disposed vertically.

6. The apparatus of claim 5 wherein the oxygen containing gas is introduced at the upper end of said chambers and the products of combustion are removed from the bottom ends thereof, and said -batts are superimposed on upon another and are moved upwardly between said chambers.

7. The apparatus of claim 6r, further comprising means for inserting the batts at the lower end of the kiln and means for removing the batts from the upper end of the kiln.

8. The apparatus of claim 7, further comprising n loading conveyor co-operating with said means for inserting and an unloading conveyor rco-operating with said means for removing.

9. The apparatus of claim 4, wherein said heating chambers are elliptical in cross-section.

10. The apparatus of claim 9, wherein said chambers extend the length of the kiln.

References Cited UNITED STATES PATENTS 2,071,015 2/1937 Andrews 34-155 2,175,866 10/1939 Arnold. 2,691,515 10/1954 Nesbitt 263--6 FREDERICK L. MATTESON, IR., Primary Examiner.

E. G. FAVORS, Assistant Examiner.

U.S. Cl. X.R. 263-52 

